This invention relates to a process for the production of polymorph III of isotactic polybutene-1, said polymorph having an orthorhombic crystal structure.
It is known that isotactic polybutene-1 crystallizes in three polymorphic forms (Chim. e Ind., Milano, 43, 735 [1961]). From the melt, there is first obtained the unstable polymorph II and, after being stored at room temperature for one to ten days, is converted into the stable high-melting polymorph I. Polymorph III can be obtained from solutions of polybutene by crystallization, precipitation, freeze-drying or evaporation ("Kunststoffe" [Plastics] 55, 431 [1965]). Such processes, however, are very expensive and result in mixtures of the various polymorphs wherein polymorph III exists only in minor quantities. (In the prior art, the term "modification" is used interchangeably with the term "polymorph", and the two terms are intended to be synonomous also in the present invention.)
The most unusual property of polymorph III is its melting range of 90.degree.-96.degree. C as compared to 120-126 for II and 130-140 for I. Accordingly, polymorph III is particularly amenable to certain end-use processes, such as coating processes, especially fluidized bed coating and also for rotational casting. Moreover, since polymorph III, although stable below the melting point, is transformed later into the polymorph I (after first passing through polymorph II), the finished parts exhibit the advantageous properties of polymorph I, namely, high melting range, higher strength, higher hardness.
In addition to the fact that polymorph III can be processed under less severe conditions, another advantage is that due to its good solubility in hydrocarbons and chlorinated hydrocarbons, polymorph III is especially suitable for the production of polybutene adhesives and can be easily employed as a starting material in chemical reactions, such as chlorination processes.